Conventional objectives in the design of internal combustion engines, especially those for use in aircraft, are to increase the horsepower-to-weight ratio, reduce wear and vibration, reduce the number of engine parts, reduce the cost of the engine, and make the engine more producible, requiring as little capital expense as possible to tool and mass produce the necessary parts. This is a very large order indeed, and the substantial number of engines of different types which have been designed and built testifies to the complexity of the problems.
The relatively small number of manufacturers of larger engines reflects the large capital costs inherent in building a conventional engine. For example, the manufacture of crankshafts and rods requires costly dedicated machinery equipment, well beyond the resources of small companies. If a smaller company does build a substantial engine which uses standard crankshafts and rods, it must buy these parts outside and contend with long lead times, inflexible production schedules, and excessive inventory costs. Furthermore, there still may remain the problems of grinding, milling, and balancing. A solution, of course, is to design an engine without a conventional crankshaft or conventional rods.
By means of this invention, the crankshaft may be replaced by a swash plate which directly converts the reciprocation of pistons to rotation of an output shaft, by means of connecting rods which can have simple clevis-type attachments at both ends. By so doing, a simple forged rod is enabled to be used which does not require the extensive grinding and honing that conventional rods require, especially when one end must be split to be installed on a crankshaft throw bearing.
A 200 horsepower engine according to this invention requires only about 60 hours of machining and assembly time, compared to about 175 hours to build a comparable four-cycle engine, using the "tool room" method of manufacture.
However, an engine according to this invention is not merely more producible for less cost and with less capital invested. In addition it enables a group of two-cycle engine elements to be linked to a pressurized induction system that is independent of the crankcase, and which can utilize turbochargers or superchargers without needing conventional combustors, and without the expensive and sensitive fuel controls that are used in conventional pressurized turbine engine systems. In this invention, the two-cycle engine elements function as the combustor, and simple carburetion techniques suffice for the fuel control. Furthermore, the engine is easily started with the use of starter motors which are light enough that they do not constitute a serious weight disadvantage even in an air-borne unit.
Especially for engines to be used in aircraft, the cross-section facing the oncoming airstream should be minimized. This engine is quite compact, with high-density placement of its components.
Conventional two-cycle engines generally require an over-square relationship between the diameter of the cylinder and the length of the piston stroke--the stroke length being shorter than the diameter of the cylinder. As a consequence, such engines generally run at higher RPMs, for example between about 6,000-8,000 RPM. This results in a very high piston surface foot per minute rate, with consequential accelerated wear and loss of energy to friction. The instant engine is able to be built under-square, with a stroke which is longer than the bore diameter, and still maintain efficient power. Therefore it can operate at a slower speed--about 4,500 RPM at a considerable saving in wear and in friction losses. By way of comparison, a conventional engine consumes about 25% of its developed energy in overcoming internal friction. In the instant engine, this loss is closer to 10%.
In addition to the foregoing advantages, this engine utilizes an improved central exhaust valve linked directly to the output shaft. A simple central exhaust gas collector, and a simplified single induction manifold are also used. These reduce the cost of the engine. No longer need the engine be surrounded by hot pipes which are subject to cracking and radiate heat which heats incoming fuel charges.
Also, cooling of the engine is radically simplified by a central porting and distribution system. It is especially efficient in its cooling of the engine at the cylinder exhaust ports. Even further, the induction system can be disposed around the outside of the engine where it can be kept cool. As a consequence of the foregoing, an efficient engine is provided which can economically be produced, and whose performance more readily relates to a turbine engine than to a reciprocating-type engine. It may properly be regarded as the "Poor Man's Turbine," and constitutes an important stride in freeing the small manufacturer from the serious economic limitations that are inherent in the manufacture of conventional reciprocating engines.